This invention relates to automatic systems for inspecting bearing balls and, more particularly, to opto-electronic systems for inspecting bearing balls which have a specularly-reflecting convex surface.
A defect in a bearing ball is likely to cause failure of a costly and complex device in which a ball bearing containing the defective ball is incorporated. For this reason, it is essential that each manufactured bearing ball be inspected for defects before being incorporated in a device. Defects include pits, burrs, scratches, scuffs and rust spots in the convex (spherical) surface thereof. In order to minimize friction, the spherical surface of a bearing ball is normally polished to a high degree so that the bearing ball surface operates as a convex mirror the specularly reflects incident light.
In the past, trained personnel visually inspected each manufactured bearing ball for defects in the surface thereof. This is relatively slow and, therefore, a relatively costly operation. Further, a small but still significant number of false positives (a defective bearing ball being found to be acceptable) occur with visual inspection.
More recently, automatic bearing ball inspection systems, including opto-electronic systems, have been developed for the purpose of increasing both the speed and reliability of inspection, thereby reducing the cost of inspection.
Prior-art opto-electronic bearing ball inspection systems illuminate each of one or more spots of the specularly-reflecting convex surface of a bearing ball under test with an incident beam of non-diffuse (e.g., "point source" light). One or more suitably placed light detectors receives light specularly-reflected from a corresponding one of the illuminated spots of the convex (spherical) surface of the bearing ball under test. Electronic means coupled to each of the light detectors measures the light intensity received thereby. A defect occurring at any illuminated spot of the bearing ball surface will scatter or absorb the incident light, rather than specularly-reflecting it. This will result in a modification of the light intensity received by at least one light detector. The electronic means, noting a modification in the light intensity, will indicate whether the bearing ball under test is defective, and preferably actuate accept-reject mechanical ball-separation means for removing the defective bearing ball under test.
In order to insure that substantially each and every spot on the entire spherical surface of the bearing ball under test is effectively illuminated by an incident light beam, the bearing ball under test is moved in a predetermined ordered manner with respect to both the incident light beam source or sources and the suitably-placed light detector or detectors. In accordance with one prior-art technique, the bearing ball under test is simultaneously rotated about each of two perpendicular axes at two appropriate different predetermined angular velocities by means of a suitable differential mechanism. In accordance with another prior-art technique, the bearing ball under test is rolled at a constant predetermined angular velocity down a pair of horizontal track rails. The two track rails are separated from one another by a distance which is only very slightly less than the diameter of the bearing ball under test. The result is that in rolling a full revolution, the bearing ball under test will translate horizontally on the track by a very small distance (i.e., the ratio of angular velocity to the translational velocity of the bearing ball under test is very large). The prior-art opto-electronic bearing ball inspection system employing the aforesaid second-mentioned technique for moving the bearing ball under test is stated to have a sensitivity sufficient to detect a defect having a dimension of 10 mils (0.01 inches) or larger.